Examples of the fluid machine include a centrifugal compressor which pressure feeds a fluid. The centrifugal compressor includes a casing, an impeller placed rotatably inside the casing, and a driving unit capable of rotating the impeller. By rotating the impeller by means of the driving unit, the fluid is taken inside the casing from the front side of the impeller in the direction along the impeller axis. The fluid is then pressure-fed to the outer side of the impeller in the radial direction to be discharged outward from the casing.
For example, a centrifugal-compressor impeller is described in Patent Literature 1. The centrifugal-compressor impeller described in Patent Literature 1 has a notch provided along a blade root. The notch is made between a blade and an adjacent blade located on the rear of the blade in the direction of blade rotation. With this configuration, a secondary flow having flowed along a surface of a hub to the notch flows through the notch to be drawn to the back side of the hub. As a result, a low-energy fluid stagnating on the suction surface side of the blade is reduced.